Molecular phylogenetics of Aspidiotini armored scale insects (Hemiptera: Diaspididae) reveals rampant paraphyly, curious species radiations, and multiple origins of association with Melissotarsus ants (Hymenoptera: Formicidae

Authors: Schneider, Scott; OKUSU, AKIKO - University Of Massachusetts; NORMARK, BENJAMIN - University Of Massachusetts

Submitted to: Molecular Phylogenetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2018
Publication Date: 9/6/2018
Citation: Schneider, S.A., Okusu, A., Normark, B.B. 2018. Molecular phylogenetics of Aspidiotini armored scale insects (Hemiptera: Diaspididae) reveals rampant paraphyly, curious species radiations, and multiple origins of association with Melissotarsus ants (Hymenoptera: Formicidae. Molecular Phylogenetics and Evolution. 129:291-303.

Interpretive Summary: Many species of armored scale insects are globally invasive and damaging to agriculture, causing billions of dollars in economic losses annually. Providing the means for reliable identification of damaging pest species is of paramount importance to agricultural research and could have lasting impact on pest management initiatives. This article uses DNA evidence to test the classification of armored scale insects from a highly diverse subgroup. Results from this study will be instrumental in ongoing efforts to improve the classification system for this important group of species. The results will also contribute toward developing identification tools using DNA data that can help in identifying established and emerging invasive pests, especially for life stages that cannot be identified by morphology. Armored scale insects also serve as model systems for a host of basic evolutionary questions. This work will contribute to both applied and basic fields of scientific research.

Technical Abstract: The armored scale insect tribe, Aspidiotini, comprises many pest species that are globally invasive and economically damaging. The taxonomy of scale insects is based almost solely upon morphological characters of adult females, and little prior work has been done to test the classification of aspidiotines against molecular evidence. Taxonomic issues within this group are consequential because of the impacts that pest species have on agricultural productivity and international trade, as well as their importance to basic research. To address these concerns, we reconstruct a molecular phylogeny for aspidiotine armored scales that expands greatly upon taxonomic and character representations from previous studies. Our dataset includes 127 species (356 terminal taxa) and four gene regions: 28S, EF-1a, COI-COII, and CAD. Nearly 50% of the taxa treated are identified as pests and several more may represent emerging pests. Phylogenetic data were analyzed in a Bayesian framework using MC3 iterations implemented in MrBayes 3.2.6. The majority of sampled aspidiotine genera are not monophyletic as currently defined. Monophyletic constraints for "worst-offenders" were imposed on the phylogeny and stepping-stone MCMC was performed to calculate marginal likelihood scores. Comparisons of marginal likelihoods from runs with constrained vs. informative priors confirm that pest-rich genera are not monophyletic. We use character mapping in Mesquite 2.75 to illustrate signal and convergence for select genus-diagnostic traits; the insights drawn could provide useful guidance in future revisionary works. Extremely polyphagous pests – typically having large populations and wide geographical distributions – are frequently intertwined with range-limited specialists on the phylogeny. These species complexes could serve to test the phylogenetic meristem hypothesis: persistent polyphagous pests could give rise to ephemeral specialists through nonadaptive radiation. Lastly, our phylogeny shows a long history of symbiosis with ants for 3 aspidiotine lineages, punctuated by opportunistic switches to novel partners.